Long-term treatment of CTCL with the oral PNP inhibitor, forodesine

Abstract

8552 Background: Forodesine is a potent inhibitor of purine nucleoside phosphorylase (PNP) that leads to T-cell selective intracellular accumulation of dGTP, resulting in apoptosis. Methods: An open-label dose escalation study of oral forodesine (40–320 mg/m2 daily) for 4 wks with extended therapy was performed to determine the maximum tolerated and/or optimal biologic dose (OBD). Additional subjects were accrued at an OBD (80 mg/m2) to further assess safety and clinical efficacy. Subjects with refractory CTCL, stages IB-IV were eligible. The primary efficacy endpoint (objective response rate [ORR]) was defined as ≥ 50% improvement by a severity-weighted assessment tool (mSWAT). Results: The overall intent to treat response rate was 17 of 64 (27%) subjects or 14 of 36 (39%) at the OBD. As of October 2008, nine of 64 subjects (14%) have received forodesine treatment for >12 months. This cohort of 9 subjects is further examined. Six discontinued treatment (median time on treatment 440 days): 4 for progressive disease, 1 withdrew consent, and 1 due to an adverse event (Diffuse Large B-cell Lymphoma). Three are continuing on therapy for 416, 710, and 863 days. Median age was 68 years (range 42, 81), and all but one was ≥ stage III. They had received a median of 3 prior systemic therapies including 8 of 9 with prior bexarotene. Five of 9 subjects had a response (2 with complete response, 3 with partial response, and 4 with stable disease). Related AEs were experienced by 7 of 9 subjects. The most frequent were nausea (44%), fatigue, peripheral edema, dyspnea, and urinary casts (all 22%). Grade 3 or higher related AEs were experienced by 2 of 9 subjects (Diffuse Large B-Cell Lymphoma as previously mentioned and peripheral edema). There were no hematologic or infection AEs related to forodesine. Grade 3 lymphopenia and CD4 count < 200 were noted in 8 of 9 and 4 of 9 subjects respectively. The risk of any infection AE regardless of cause in these 9 subjects was 15 per 100 person-months of forodesine exposure compared to 59 in all other subjects (n=55). Conclusions: Forodesine has an acceptable safety profile and efficacy in these CTCL subjects treated for 12 months or longer. [Table: see text]